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The advantages and application of various valves

2018/9/21 17:56:56 Viewers:
Gate valve: Gate valve refers to the closing parts (gate) along the channel axis of the vertical direction of the valve movement, in the pipeline mainly as a cut-off medium, that is, all open or all closed use. Generally, gate valves can not be used as regulating flow. It can be applied to low temperature pressure, can also be applied to high temperature and high pressure, and according to the valve's different material. But gate valves are generally not used for pipes conveying mud and other media.


Advantages: 1) low fluid resistance; 2) small torque required for opening and closing; 3) can be used in the ring network pipeline where the medium flows in two directions, that is, the flow direction of the medium is not restricted; 4) when fully opened, the sealing surface is less eroded by the working medium than the globe valve; _the shape structure is relatively simple, and the manufacturing process is better;structure; The length is shorter.


Disadvantages: 1) large size and opening height, the installation space is also large; 2) in the process of opening and closing, the sealing surface relative friction, friction, and even in high temperature easy to cause scratches; 3) general gate valves have two sealing surfaces, machining, grinding and maintenance to increase some difficulties; 4) opening and closing time Long between.


Check valve: also called counterflow valve, check valve, back pressure valve and check valve. These valves are automatically opened and closed by the force generated by the flow of the medium itself in the pipeline, belonging to an automatic valve. Check valves are used in pipeline systems. Their main functions are to prevent medium backflow, pump and drive motor reversal, and container media release. Check valves can also be used to supply lines in which the pressure may rise to an auxiliary system that exceeds the system pressure. It can be divided into swing type (center of gravity rotation) and lifting type (along the axis).


Globe valve: the valve that closes the valve along the center line of the valve seat. According to the moving form of the disc, the change of the valve seat opening is proportional to the valve stroke. Because the stem opening or closing stroke of this kind of valve is relatively short, and has a very reliable cut-off function, and because the change of seat opening is proportional to the disc stroke, it is very suitable for flow regulation. Therefore, this type of valve is very suitable for cutting or regulating and throttling.

Advantages: 1. In the process of opening and closing, the friction between the disc and the sealing surface of the valve body is smaller than that of the gate valve, thus wearing resistance. The opening height is generally only 1/4 of the seat passage, so it is much smaller than the gate valve; 3. There is usually only one sealing surface on the valve body and disc, so the manufacturing process is better and easy to maintain. Fourth, because its filler is generally a mixture of asbestos and graphite, the temperature resistance grade is higher. General steam valves are globe valves.

Disadvantages: 1) Because the flow direction of the medium through the valve has changed, the minimum flow resistance of the globe valve is also higher than that of most other types of valves; 2) Because of the longer stroke, the opening speed is slower than that of the ball valve.


Ball valve: is evolved from the plug valve, its opening and closing parts is a ball, the use of the ball around the axis of the stem rotating 90 degrees to achieve the purpose of opening and closing. Ball valve is mainly used to cut off, distribute and change the flow direction of the medium in the pipeline. The V-shaped open ball valve also has good flow regulation function.


Advantages: 1) having the lowest flow resistance (actually 0); 2) being able to reliably apply to corrosive media and low boiling point liquids because it is not stuck in operation (without lubricant); 3) being able to achieve complete sealing in a wide range of pressure and temperature; 4) being able to achieve rapid opening and closing, and the opening and closing time of some structures is only 0. .05~0.1s, to ensure that it can be used in the automation system of the test stand. When the valve is opened and closed fast, the operation is not affected. _Spherical closure can be positioned automatically at the boundary position; _Working medium is sealed reliably on both sides; _When the ball and the valve seat are fully opened and closed, the sealing surface is isolated from the medium, so the medium passing through the valve at high speed will not cause the erosion of the sealing surface; _Compact structure, light weight, it can be considered to be used in low temperature medium. The most reasonable valve structure of the quality system; _valve body symmetry, especially the welding valve body structure, can withstand the stress from the pipeline; _closing parts can withstand the high pressure difference when closed. _Fully welded ball valve body, can be directly buried underground, so that the valve internals are not eroded, the maximum service life of up to 30 years, is the best valve for oil and natural gas pipelines.

Disadvantages: 1. Because the main seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemicals, and has the comprehensive characteristics of low friction coefficient, stable performance, not easy to aging, wide temperature range of application and excellent sealing performance. However, the physical properties of PTFE, including high coefficient of expansion, sensitivity to cold flow and poor heat conductivity, require the design of seat seals must be around these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal will be destroyed. Moreover, PTFE has low temperature resistance and can only be used at less than 180 degrees centigrade. Beyond this temperature, the sealing material will wear out. Considering the long-term use, it will not be used at 120 degrees. Its adjustment performance is worse than that of the globe valve, especially the pneumatic valve (or electric valve).

Diaphragm valve: refers to the valve body and valve cover with a flexible membrane or combination of diaphragms, its closure is connected with the diaphragm of a compression device. The valve can be weir shaped or straight through the pipe wall.